Bit error rate (BER) estimation of transport channels is a measure of transport channel quality, based on which the Radio Access Network could take actions to improve the quality of certain transport channels if needed. The 3GPP standards contain strict requirements for such estimations. Below in table 1, one of the requirements taken from the 3GPP standard 25.215 is listed.
TABLE 1DefinitionThe transport channel BER is an estimation of the averagebit error rate (BER) of the DPDCH data of a Radio Link Set.The transport channel (TrCH) BER is measured from the dataconsidering only non-punctured bits at the input of thechannel decoder in Node B. It shall be possible to reportan estimate of the transport channel BER for a TrCH afterthe end of each TTI of the TrCH. The reported TrCH BERshall be an estimate of the BER during the latest TTI forthat TrCH.
The average of consecutive Transport channel BER measurements is required to fulfil the accuracy stated in table 2 below if the total number of erroneous bits during these measurements is at least 500 and the absolute BER value for each of the measurements is within the range given in the table 2.
TABLE 2Accuracy[% of theabsoluteConditionsParameterUnitBER value]RangeTrpBER—+/−10Convolutional coding ⅓rd with anyamount of repetition or a maximumof 25% puncturing:for absolute BER value ≤15%Convolutional coding ½ with anyamount of repetition or no puncturing:for absolute BER value ≤15%Turbo coding ⅓rd with any amountof repetition or a maximum of 20%puncturing:for absolute BER value ≤15%.
At present two main methods of doing the BER measurement are known: a so-called straight forward (brute force) method and a SNR to BER conversion technique. The straight forward method exploits the fact that the data, for which the BER is measured, is coded using error correction codes. By decoding this data, the errors or part of the errors will be corrected. Having the corrected decoded data, it can be re-encoded and used as reference to detect the erroneous bits. This method requires re-encoding to be performed which is very computationally intensive. Furthermore, the point of measurement is after the Decoding stage. This has larger latency. Also the performance of the estimate is dependent of the used decoder.
The SNR to BER conversion method estimates the BER exploiting the correlation between SNR, BER and the shape of the distribution of noise. It comprises 2 main stages: estimating the SNR and next translating the SNR to BER. The translation from SNR to BER can be deduced when the shape of the noise distribution is known. The main disadvantage of this method is that it assumes that the noise distribution is known in order to do the conversion. This is not always possible in real case scenarios.